Abstract:
The objective of this project was to design and fabricate a printed circuit board that would emulate a traffic light. Light emitting diodes (LEDs) were used for the green, yellow and red lights of the traffic light. The lighting of the LEDs was timed using a combination of a counter IC and a timing IC. The timing and lighting order was set to emulate a UK traffic light, with timing controllable by a potentiometer.
The goal of this project was to design and build a traffic light. A schematic and description was based on a kit by RSH Electronics. The traffic light emulates a UK traffic light. To time the traffic light, a 555 timer IC was used in its astable mode to generate pulses. When wired as shown in figure 1, the IC puts out rectangle pulses with a given frequency. R2 is connected to another resistor R1 as well as a capacitor. In this arrangement, the capacitor is charged through R1 and R2, but only discharged through R2. The frequency is modified by changing the values of R1, R2, and C. For this project, the resistance of R2 in the figure was changed by using a potentiometer.
Figure 1: 555 Timer in Astable Mode
The pulses generated by the 555 timer were fed into a decade counter. A 4017 decade counter was used in this case. To time the three LEDs, the outputs in figure 2 were used.
For the first five counts (Q0-Q4) the ÷10 counter has a high output, then the count cycles through the next five counts (Q5-Q9). The LEDs were connected to the IC as shown in figure
2. For UK traffic lights, both red and yellow lights are illuminated at the same time before transitioning to green. To eliminate this for a US traffic light, the yellow LED connected to
Q4 could be eliminated, but I chose not to for this project.

Figure 2: 4017 Counter outputs
The schematic is shown below in figure 3. Power was supplied by a 9V battery, and the device is turned on and off with a switch.
Figure 3: Schematic of Traffic Light
The schematic was turned into a board layout. To simplify assembly and align the LEDs, the traces were put on both sides of the board. The layout is shown in figure 4, with silkscreen in green, top traces in black, and bottom traces in grey. For ease of assembly, only throughhole components were used.

Figure 4: Board Layout
After the layout was sent off to be manufactured, the board was assembled. Upon assembly, I recognized that the vias for the resistors were slightly too small, but I was still able to push the leads through. I also found that the pattern for the switch was dimensioned incorrectly, which necessitated cutting off the unused lead and bending the mounts to fit the board. This did not affect the operation of the board.

Figure 5: Assembled Board
The project resulted in a functional printed circuit board that emulates a UK traffic light.
When the switch is turned on, the lights illuminate in the correct order and have the correct timing. The timing can be adjusted using the potentiometer, from approximately 10 seconds for the full cycle up to approximately one minute.
From this project I learned how to turn a schematic into a functional circuit board, as well as the considerations that must be made along the way to have the board function properly.
If the project were to be done again, I would pay closer attention to dimensioning the components when making patterns. Otherwise, this project was a straightforward approach to emulating a traffic light.

BOM
Ite m #
Qt y
2 1
3 1
4 1
5 1
6 1
Reference
Designator
1 3 R1, R2, R3
R4
R5
C1
C2
C3
Type
Resistor
Resistor
Resistor
Value/Part
#
470 Ω,
Packag e Type
Manufactur er
Axial Std
1/4W, ±5%
22kΩ, Axial Std
1/4W, ±5%
100kΩ, Axial Std
1/4W, ±5%
Capacitor 0.1 uF Through
-Hole
Std
Polar
Capacitor
Polar
Capacitor
Diode
1uF 50V radial
10 uF 25V radial
Through
-Hole
Through
-Hole
Std
Std
1N4148 Axial Philips
Manufacturer/Par t#
7 6 D1,D2,D3,D4,D5,
D6
8 1 LED1
9 1
10 1
11 1
12 1
13 1
16 1
17 1
18 1
LED2
LED3
VR1
U1
U2
K1
J1
LED
LED
Green,
3mm
Yellow,
3mm
Through
-Hole
Std
Through
-Hole
Std
LED Red, 3mm Through
-Hole
Std
Potentiomet er
1M, horizontal
Timer IC NE555
Counter IC 4017
Switch
Through
-Hole
Alpha
DIP-8 Texas
Instruments
DIP-16 Texas
Instruments
POT1MB
NE555P
CD4017BE
1P2T 0.5A
50VDC
Through
-Hole
Wealth Metal SS12F45G8
Std Std Cable, 9V,
Battery
Snap
Plastic
Knob,
Potentiomet er
Std Std